Blood flow and oxygen consumption in human cerebral cortex continues to be of great scientific interest due to their importance in understanding brain pathophysiology and their central role in mapping human brain function. Recently, we have found that oxygen extraction fraction (derived from the ratio of oxygen consumption to blood flow) is an excellent indicator of an acute change in neuronal activity, but sustained activity appears to alter the relationship of oxygen metabolism of blood flow. This project proposes to solidify and expand these preliminary observations. The overarching goal will be to characterize more complete the relationship of regional blood flow and oxygen consumption in the brain. The dependence of this relationship on three important variables will be examined. First, in Specific Aim 1 the regional dependence of this relationship on three important variables will be examined. First, in Specific Aim 1 the regional relationship of blood flow and oxygen consumption in the resting brain will be measured with attention to the differences between deactivated, activated and baseline brain states. Second, the time-dependence of the relationship between blood flow and oxygen consumption after a change in neuronal activity level will be measured. This will be examined using laboratory induced changes in neuronal activity in Specific Aim 3 and naturalistically by studying victims of stroke in Specific Aim 4. The third area of emphasis will be to examine the effect of age on this time-dependence as part of Specific Aims 2 and 3. Numerous adaptive processes in the body are slowed with aging and the impact of aging on the time-dependence of OEF changes may be substantial.